ImportError: cannot import name 'FileStorage'

Following the docs shown on https://pypi.org/project/wes-service/, I just installed via 'pip install wes-service' into a python 3.6 virtual env. When I run 'wes-server' I get the error:
```
$ wes-server
Traceback (most recent call last):
File "/Users/golharr/workspace/ga4gh/wes-env/bin/wes-server", line 7, in
from wes_service.wes_service_main import main
File "/Users/golharr/workspace/ga4gh/wes-env/lib/python3.6/site-packages/wes_service/wes_service_main.py", line 8, in
import connexion
File "/Users/golharr/workspace/ga4gh/wes-env/lib/python3.6/site-packages/connexion/__init__.py", line 3, in
from .apis import AbstractAPI # NOQA
File "/Users/golharr/workspace/ga4gh/wes-env/lib/python3.6/site-packages/connexion/apis/__init__.py", line 1, in
from .abstract import AbstractAPI # NOQA
File "/Users/golharr/workspace/ga4gh/wes-env/lib/python3.6/site-packages/connexion/apis/abstract.py", line 14, in
from ..operation import Operation
File "/Users/golharr/workspace/ga4gh/wes-env/lib/python3.6/site-packages/connexion/operation.py", line 7, in
from .decorators import validation
File "/Users/golharr/workspace/ga4gh/wes-env/lib/python3.6/site-packages/connexion/decorators/validation.py", line 9, in
from werkzeug import FileStorage
ImportError: cannot import name 'FileStorage'
```

Reproduce the installation in a Python 3.6 virtual environment with `pip install wes-service`, then run the `wes-server` entry point. Trace the import path through `wes_service/wes_service_main.py` into Connexion's `decorators/validation.py`, where `werkzeug.FileStorage` fails to import. Done means `wes-server` starts without this ImportError.

Written by the indexing model from the issue text.